This invention pertains to ignition systems and, more particularly, to piezoelectric ignition systems in which a sustained spark is provided.
The reduction of atmospheric NOx is a high priority as it contributes significantly to urban smog and other unwanted pollution, i.e., acid rain. Despite ongoing research and development efforts to reduce the emissions of the oxides of nitrogen (NOx) from road surface vehicles, their engines still remain one of the largest producers of ozone forming pollutants in the world. Significant progress has been made to reduce the emissions from light trucks and passenger vehicles since the introduction of the Clean Air Act in 1990. However, even with today""s standards, the EPA predicts that these vehicles will produce more than 40% of the ozone-forming pollutants in major cities by the year 2030.
New regulations recently issued by the EPA call for a reduction in NOx produced by new passenger vehicles to 0.07 grams per mile by 2007. This implies a reduction in NOx of 856,000 tons per year by 2007. Most of the technologies that will be implemented to achieve this goal have been demonstrated during the National Low Emissions Vehicle (NLEV) program. Although most are still in the research phase, it is postulated that the demonstrated technologies will have enough maturity to fulfill these emission requirements. However, the new regulations apply only to new vehicles. The vast majority of vehicles on the road is older and thus not subject to these new reductions.
Thus, it is desired to have a method of reducing emissions that can easily be integrated into older vehicles.
The invention described here presents an alternative to the reduction of NOx that can easily be integrated into existing vehicles and will extend the controllability of new engines. The invention enables extension of the lean burn limit of gasoline, an increase in the burning rate of gasoline and recycled exhaust gas concentration, and a reduction of cycle by cycle variations in the cylinder. All these factors combine to reduce the mass of NOx per horsepower that the engine delivers. The technology can be incorporated into both new automobiles and current spark ignition engines.
In one aspect, the invention is an ignition circuit. The circuit comprises a piezoelectric element, a capacitor, and a spark gap connected in parallel. The piezoelectric element generates a voltage sufficient to produce a spark to cause dielectric breakdown in a fuel-air mixture in response to an increase in the pressure of said mixture, and the voltage of a charge stored on the capacitor is sufficient to traverse the spark gap after dielectric breakdown. The capacitor may be charged by a DC power source, which may comprise an AC power source and a bridge rectifier. The AC power source may provide 12V, and the source of DC power may further comprise a 1:40 transformer. The circuit may comprise a plurality of capacitors in parallel with one another, and the piezoelectric element may comprise a plurality of sub-elements that combine to generate a voltage equal to the sum of the voltages developed by each sub-element. The charge stored on the capacitor may be sufficient to sustain a spark generated by the voltage from the piezoelectric element. The circuit may further comprise a timing circuit in electrical communication with the piezoelectric element, wherein spark timing is determined using voltage information from the piezoelectric element.
In another aspect, the invention is a method of igniting a spark. The method may comprise exerting pressure on a piezoelectric element to generate a voltage, placing the piezoelectric element in electrical communication with a spark gap, wherein the voltage across the piezoelectric element is sufficient to cause a spark across a spark gap, and directing current from a capacitor to the spark gap, wherein the current has sufficient energy to traverse the spark gap. The energy of the spark resulting from the voltage supplied by the piezoelectric element may be sufficient to ignite a fuel-air mixture, and the step of exerting pressure may comprise compressing,the fuel-air mixture. The spark voltage supplied by the piezoelectric element may have a voltage at least a factor of 10, 50, 100, 1000, or 4000 greater than the spark voltage supplied by the capacitor.
In another aspect, the invention is a method of increasing energy delivery to a fuel-gas mixture. The method comprising causing dielectric breakdown in the fuel-gas mixture, thereby reducing impedance of the mixture and supplying current having a voltage sufficient to bridge a spark gap through the reduced impedance mixture.